1. Field of the Invention
The present invention relates to a silver halide photographic material and a process for forming images, particularly a black-and-white photographic material involving the use of dye images which can be processed with a color developer substantially free from benzyl alcohol and little suffers from the deterioration of photographic characteristics by harmful gas such as formaldehyde and a process for forming images.
2. Description of the Prior Art
It is a usual practice in the recent daily life to use furniture or building materials modified with formaldehyde, adhesives containing formaldehyde as the curing agent, articles processed with formaldehyde resins, formaldehyde-tanned leather products, clothes containing formaldehyde as a bactericide or bleach, and so on. Therefore, the chance has increased that photographic materials come into contact with formaldehyde discharged from these materials or products.
In general, a silver halide color photographic material comprises a base and several silver halide emulsion layers formed on the base containing couplers which react with an oxide of a color developing agent to form dyes, i.e., silver halide layers which exhibit sensitivity for blue, green and red lights and contain a yellow coupler, a magenta coupler and a cyan coupler, respectively, and in these silver halide emulsion layers, images of yellow, magenta and cyan dyes are respectively formed through exposure and color development.
In order to obtain a good color picture, such a multilayer color photographic material is required to be well-balanced among the silver halide emulsion layers with respect to sensitivity and tone, and is desired not to cause any change in the photographic performance during storage up to color development, inclusive of the terms before and after exposure.
When a silver halide color photographic material comes into contact with formaldehyde gas before color development, however, the couplers are consumed by the reaction with formaldehyde through the formation of undesirable reaction products, which brings about deterioration of photographic characteristic such as lowered densities of formed dyes or significant color stain or fog. The deterioration of the photographic characteristic by formaldehyde gas is remarkable when a so-called four-equivalent coupler having an active methylene group is used. In particular, magenta couplers are liable to be more significantly affected by formaldehyde.
In order to inhibit the deterioration of the photographic characteristic by formaldehyde gas, attempts have been made to incorporate compounds reactive with formaldehyde into coupler-in-emulsion type silver halide color photographic materials. Up to this time, many compounds have been proposed in, e.g., JP-B 46-34675, 48-38418 and 51-23908 and U.S. Pat. No. 3,770,431 as the compounds effective in protecting the silver halide color photographic materials containing oil-soluble four equivalent magenta couplers from the deterioration of the photographic characteristic by formaldehyde gas. However, these compounds had disadvantages in that the power of immobilizing formaldehyde gas was too poor to attain any satisfactory effect and that the addition of the compounds in large amounts was causative of lowering in the film properties of the photographic material.
Meanwhile, photographic systems forming black-and-white images by using combinations of cyan, magenta and yellow dyes have also been known (see, e.g., JP-A 6-505580). In such a system, dyes are made from a mixture of cyan, magenta and yellow color-forming couplers during color development, and the couplers give neutral images when reacted with an oxidized color developing agent. However, the above patent document (JP-A 6-505580) is silent on formaldehyde gas or compounds reactive with formaldehyde gas.
The inventors of the present invention have found that a magenta coupler is affected by formaldehyde gas even in such photographic systems of forming black-and-white images by using combinations of cyan, magenta and yellow dyes.
Further, the formation of black-and-white images by using silver images according to the prior art was conducted through development with a black-and-white developing agent such as hydroquinone. However, there are few laboratories and camera shops wherein such development can be conducted. Meanwhile, the processing of color papers is currently conducted by using a color developer substantially free from benzyl alcohol, and machines suitable for this processing have widely been spread to many laboratories and camera shops. Black-and-white image forming materials processable by such machines are favorable under these circumstances.
The first object of the present invention is to provide a silver halide photographic material giving a black-and-white picture by the use of dye images in which the contained magenta coupler is little affected by formaldehyde gas.
The second object of the present invention is to provide a process for forming images which can give a black-and-white picture by the use of dye images through development with a color developer substantially free from benzyl alcohol.